linux-kernel - Re: [PATCH v7 0/8] x86/kexec: Add exception handling for relocate

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Message-ID: <Z9QDP5NHp-5VupUS@gmail.com>
Date: Fri, 14 Mar 2025 11:21:51 +0100
From: Ingo Molnar <mingo@...nel.org>
To: David Woodhouse <dwmw2@...radead.org>
Cc: kexec@...ts.infradead.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Kai Huang <kai.huang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	linux-kernel@...r.kernel.org, Simon Horman <horms@...nel.org>,
	Dave Young <dyoung@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, jpoimboe@...nel.org,
	bsz@...zon.de
Subject: Re: [PATCH v7 0/8] x86/kexec: Add exception handling for
 relocate_kernel


* David Woodhouse <dwmw2@...radead.org> wrote:

> On Thu, 2025-03-13 at 19:58 +0000, David Woodhouse wrote:
> > 
> > Reproduced that by going back to x86-64 defconfig. 
> 
> Turns out the unret check doesn't even run unless CONFIG_DEBUG_ENTRY is
> enabled (which enables CONFIG_NOINSTR_VALIDATION and thus runs objtool
> on vmlinux.o). Which is why I didn't see it.
> 
> > vmlinux.o: warning: objtool: exc_handler+0xe: early indirect call
> 
> With Peter's help (thanks), this is fixed by adding VALIDATE_UNRET_END.
> I'll squash this into the next posting:
> 
> --- a/arch/x86/kernel/relocate_kernel_64.S
> +++ b/arch/x86/kernel/relocate_kernel_64.S
> @@ -481,6 +481,9 @@ SYM_CODE_START_NOALIGN(kexec_debug_exc_vectors)
>  SYM_CODE_END(kexec_debug_exc_vectors)
>  
>  SYM_CODE_START_LOCAL_NOALIGN(exc_handler)
> +       /* No need for ret mitigations during kexec */
> +       VALIDATE_UNRET_END
> +
>         pushq   %rax
>         pushq   %rbx
>         pushq   %rcx

Great!

I've applied patch #1 back to tip:x86/boot.

I've skipped the -v7 versions of patch #2 and #3 because AFAICS you've 
changed exc_handler already, so a backmerge of this annotation fix 
wouldn't be enough.

Thanks,

	Ingo